BRITISH STANDARD BS EN 12952 8 2002 Water tube boilers and auxiliary installations — Part 8 Requirements for firing systems for liquid and gaseous fuels for the boiler The European Standard EN 12952 8[.]
Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BRITISH STANDARD Water-tube boilers and auxiliary installations — Part 8: Requirements for firing systems for liquid and gaseous fuels for the boiler The European Standard EN 12952-8:2002 has the status of a British Standard ICS 27.040 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN 12952-8:2002 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI BS EN 12952-8:2002 National foreword This British Standard is the official English language version of EN 12952-8:2002 When the reference to this European Standard has been published in the Official Journal of the European Communities (OJ), compliance with it will confer a presumption of conformity with the essential requirements covered by the standard in respect of the Pressure Equipment Directive The UK participation in its preparation was entrusted to Technical Committee PVE/2, Water-tube boilers, which has the responsibility to: — aid enquirers to understand the text; — present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; — monitor related international and European developments and promulgate them in the UK A list of organizations represented on this committee can be obtained on request to its secretary Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online This publication does not purport to include all the necessary provisions of a contract Users of this publication are responsible for their correct application Compliance with a British Standard does not of itself confer immunity from legal obligations This British Standard, having been prepared under the direction of the Engineering Sector Policy and Strategy Committee, was published under the authority of the Standards Policy and Strategy Committee on 13 June 2002 Summary of pages This document comprises a front cover, an inside front cover, the EN title page, pages to 26, an inside back cover and a back cover The BSI copyright date displayed in this document indicates when the document was last issued Amendments issued since publication Amd No © BSI 13 June 2002 ISBN 580 39860 Date Comments Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EUROPEAN STANDARD EN 12952-8 NORME EUROPÉENNE EUROPÄISCHE NORM May 2002 ICS 27.040 English version Water-tube boilers and auxiliary installations - Part 8: Requirements for firing systems for liquid and gaseous fuels for the boiler Chaudières tubes d'eau et installations auxiliaires - Partie 8: Exigences pour les équipements de chauffe pour combustibles gazeux et liquides de la chaudière Wasserrohrkessel und Anlagenkomponenten - Teil 8: Anforderungen an Feuerungsanlagen für flüssige und gasförmige für den Kessel This European Standard was approved by CEN on 15 May 2002 CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Management Centre or to any CEN member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official versions CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG Management Centre: rue de Stassart, 36 © 2002 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members B-1050 Brussels Ref No EN 12952-8:2002 E Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) Contents Page Foreword 1.1 1.2 1.3 Scope Firing systems Fuels Operation Normative references Terms and definitions 4.1 4.2 4.3 4.4 Fuel supply 10 General 10 Fuel transfer and preparation .10 Fuel lines .10 Safety shut-off devices (Safety trip valves) .12 5.1 5.2 5.3 Equipment for air supply and flue gas discharge 13 Air supply 13 Air/fuel ratio 14 Flue gas discharge 14 6.1 6.2 6.3 6.4 6.5 6.6 Firing system 15 Burners 15 Flue gas recirculation 15 Control and monitoring .16 Electrical equipment 17 Safety precautions .17 Common stack for several firing systems 18 Operating manual 18 8.1 8.2 Particular requirements for firing systems burning gaseous fuels with high relative density 18 Main firing systems .18 Ignition burner systems 19 Annex A (normative) Chemical recovery boiler (black liquor boiler) 20 A.1 General 20 A.2 Additional requirements for the firing system for black liquor in the chemical recovery boiler 20 A.3 Special requirements for oil- or gas firing for chemical recovery boilers .21 Annex B (informative) Operational requirements for permanent supervised firing systems for liquid and gaseous fuels 22 B.1 General 22 B.2 Operation 22 B.3 Fuel preparation 22 B.4 Safety shutoff devices .22 B.5 Air/fuel ratio 22 B.6 Modification of firing, burner or air/fuel ratio setting .22 B.7 Control and monitoring .23 B.8 Purging, start-up and shut down .23 B.9 Emergency operation 23 B.10 Operating and maintenance instructions 23 B.11 Firing systems burning gaseous fuels with high relative density 23 Annex ZA (informative) Clauses of this European Standard addressing essential safety requirements or other provisions of the Pressure Equipment Directives 25 Bibliography 26 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) Foreword This document (EN 12952-8:2002) has been prepared by Technical Committee CEN/TC 269 "Shell and water-tube boilers", the secretariat of which is held by DIN This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s) For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this standard This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by November 2002, and conflicting national standards shall be withdrawn at the latest by November 2002 The European Standard EN 12952 concerning “Water-tube boilers and auxiliary installations” consists of the following Parts: Part 1: General Part 2: Materials for pressure parts of boilers and accessories Part 3: Design and calculation for pressure parts Part 4: In-service boiler life expectancy calculations Part 5: Workmanship and construction of pressure parts of the boiler Part 6: Inspection during construction, documentation and marking of pressure parts of the boiler Part 7: Requirements for equipment for the boiler Part 8: Requirements for firing systems for liquid and gaseous fuels for the boiler Part 9: Requirements for firing systems for pulverized solid fuels for the boiler Part 10: Requirements for safeguards against excessive pressure Part 11: Requirements for limiting devices of the boiler and accessories Part 12: Requirements for boiler feedwater and boiler water quality Part 13: Requirements for flue gas cleaning systems Part 14: Requirements for flue gas DENOX-systems Part 15: Acceptance tests Part 16: Requirements for grate and fluidised bed firing systems for solid fuels for the boiler CR 12952 Part 17: Guideline for the involvement of an inspection body independent of the manufacturer Although, these Parts can be obtained separately, it should be recognized that the Parts are interdependent As such, the design and manufacture of water-tube boilers requires the application of more than one Part in order for the requirements of the standard to be satisfactorily fulfilled Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) NOTE Parts and 15 are not applicable during the design, construction and installation stages Annex A of this European Standard is normative and Annex B is informative According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) 1.1 Scope Firing systems This Part of this European Standard specifies requirements, for oil and gas firing systems of steam boilers and hot water generators as defined in EN 12952-1 These requirements also apply to firing systems of chemical recovery boilers (black liquor boilers) with the additions and amendments specified in Annex A of this standard NOTE This standard is not applicable to coil type boilers (flash boilers/small boilers) that use burners in accordance with EN 12953-7 apply for single burner installations 1.2 NOTE This standard is not applicable to the storage of liquid fuels and to transfer stations of long-distance gas pipelines Fuels This Part of this European Standard specifies requirements, which cover the use of liquid and gaseous fuels as defined in this standard Fuels deviating from standardized commercially available types may require additional or alternative safety measures For black liquor these safety measures are given in Annex A 1.3 Operation This Part of this European Standard specifies requirements for operational equipment in clauses to which apply to steam boilers and hot water generators with permanent supervision by properly trained personnel familiar with the special conditions of the firing system and the type of fuel being fired Normative references This European Standard incorporates by dated or undated reference, provisions from other publications These normative references are cited at the appropriate places in the text and the publications are listed hereafter For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision For undated references the latest edition of the publication referred to applies (including amendments) EN 161, Automatic shut-off valves for gas burners and gas appliances EN 264, Safety shut-off devices for combustion plants using liquid fuels — Safety requirements and testing EN 287-1, Approval testing of welders — Fusion welding — Part 1: Steels EN 751-1, Sealing materials for metallic threaded joints in contact with 1st, 2nd and 3rd family gases and hot water — Part 1: Anaerobic jointing compounds EN 751-2, Sealing materials for metallic threaded joints in contact with 1st, 2nd and 3rd family gases and hot water — Part 2: Non-hardening jointing compounds EN 751-3, Sealing materials for metallic threaded joints in contact with 1st, 2nd and 3rd family gases and hot water — Part 3: Unsintered PTFE tapes EN 1044, Brazing — Filler metals EN 12952-1, Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) prEN 50156-1, Electrical equipment for furnaces and ancillary equipment — Part 1: Requirements for application design and installation EN ISO 3677, Filler metal for soft soldering, brazing and braze welding — Designation (ISO 3677:1992) ISO 7-1, Pipe threads where pressure-tight joints are made on the threads — Part 1: Dimensions, tolerances and designation (ISO 7-1:1994) ISO 228-1, Pipe threads where pressure-tight joints are not made on the threads — Part 1: Dimensions, tolerances and designation (ISO 228-1:2000) Terms and definitions For the purposes of this Part of this European Standard and the following terms and definitions apply 3.1 black liquor spent liquor from the pulp cook 3.2 black liquor gun device for the introduction of the black liquor as a spray of droplets into the furnace The black liquor gun is not a burner 3.3 high volume low concentration odorous gas mixtures of air and a low concentration of odorous gases collected from the pulp mill processes, where the concentration of the combustible odorous gas is always kept below the lower explosion limit 3.4 burners devices (including main or igniter burners) for the introduction of fuel and air into a combustion chamber at required velocities, turbulence and local fuel concentration to establish and maintain proper ignition and stable combustion of the fuel Burners are differentiated by their mode of operation 3.4.1 automatic burners burners equipped with automatic ignition, flame monitoring and safety control devices that control the firing rate without the intervention by operating personnel 3.4.2 semi-automatic burners burners equipped with automatic ignition, flame monitoring and safety control devices which are started and stopped by the intervention of operating personnel 3.4.3 chemical recovery boiler start up burner oil- or gasfired burner mainly intended for the initiation of the black liquor combustion process The chemical recovery boiler start up burners are located in and integrated with a combustion air register, like the primary or the secondary air register of the furnace Thus they have no individual air supply and no individual combustion air control 3.4.4 multi-fuel burners burners in which more than one fuel is burned either simultaneously or alternately 3.4.5 pilot burner burner which maintains a proper permanent ignition source for one or a group of other non-monitored burners Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) 3.5 burner group burners operated in unison and controlled jointly One of the burners can be a master burner 3.6 burner management system system that performs a predetermined sequence of actions and always operates in conjunction with a flame monitor that reacts to signals from control and safety devices, gives control commands, controls the start-up sequence, supervises the burner operation, and manages controlled shutdown and lockout 3.7 firing system total equipment required for the combustion of fuels including the installations for the storage, preparation, and supply of fuels, the combustion air supply, the burner(s), the flue gas discharge, and all related control and monitoring devices A flue gas recirculation system can be an integral part of the firing system 3.8 firing system heat input heat input into the combustion chamber according to the mass flow of the fuel supplied multiplied by the net calorific value 3.9 flame monitor device which detects the presence or absence or break-away of the flame and transmits a signal to the control device, and generally consists of a sensing device (with amplifier if necessary) and switching equipment 3.10 flue gas recirculation return of flue gas from downstream of the flame zone or from the flue gas exit by hydrodynamic pressure difference or a separate fan into the air register of the burner or directly into the combustion chamber 3.11 implosion unintentional instantaneous negative pressure build-up caused, for example, by an explosion in a confined space, by rapid closing of dampers, or by rapid reduction in temperature (flame out) 3.12 limiters transducer, which, on reaching a fixed value (e.g pressure, temperature, flow, water level) is used to interrupt and lock-out the energy supply, and requires manual unlocking before restart 3.13 lock-out isolation of energy supply which requires a manual intervention to reinstate 3.14 master fuel trip device for rapid automatic shut-off of all fuel supplies to the boiler area and electrical igniters in the event of danger which may act by automatic, manual or emergency switch initiation even if a possible electrical or mechanical fault occurs 3.15 maximum heat input of the firing system heat input including the reserve required for load control at which the boiler can be safely operated 3.16 maximum firing rate of the burners firing rate at which the burner may be operated Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) 3.17 monitor limit transducer, which senses the reaching of a fixed limit value and initiates an alarm and/or a cut out The output signal is only cancelled if the cause of the alarm has been removed and the value has returned to within its fixed limits 3.18 multi-fuel firing system firing system where, in a common combustion chamber, more than one fuel can be burnt simultaneously or alternately by separate or multi-fuel burners 3.19 purge of burner guns carried out after shutdown of a burner to ensure the removal of residual fuel by the introduction of steam or pressurized air into the fuel lines downstream of the shut-off devices 3.20 purging of the flue gas passes forced flow of air through the combustion chamber, flue gas passes, and associated ducts which effectively removes any gaseous combustibles and replace them with air 3.21 quick-acting shut-off device safety trip valve which closes within s 3.22 relative density ratio of the density of the gas to the density of dry air under equal conditions of pressure and temperature 3.23 liquid fuels fuels include light fuel oils, and heavy fuel oils which need preheating for proper atomisation For improvement of atomisation, emulsions of heavy fuel oil with water may be used with appropriate precautions 3.24 gaseous fuels standardized quality differentiated mainly by their relative density 3.24.1 light gases with relative density below 1,3 e.g natural gas, coke-oven gas, blast-furnace gas NOTE Natural gas in accordance with ISO 6976 3.24.2 heavy gases with relative densities exceeding 1,3 e.g liquefied petroleum gases, the main components of which are propane and butane 3.25 restart operation where fuel supply shut-off is initiated within s at the latest after extinction of the flame during operation, and a directly following attempt of re-ignition is automatically made in compliance with the start-up sequence This operation ends with the operating condition being reached or, if the flame is not ignited after expiration of the ignition safety time, with the lock-out Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) 3.26 return-fow atomizer oil burners, where a portion of the quantity of oil supplied to the burner via the flow line does not flow from a burner gun vortex chamber into the combustion chamber, but flows backwards into the storage tank or to the suction side of the pump via a separate return line Output is adjusted by a control device in the return line 3.27 safety shut-off device safety trip valve valve which automatically and totally cuts off the fuel supply 3.28 safety time tolerance time during which the effectiveness of the safety device may be inhibited without a hazardous condition occurring 3.28.1 ignition time: When starting-up the burner, the period of time between the first fuel entering the combustion chamber and the first indication of the flame by the flame monitor 3.28.2 ignition safety time: When starting-up the burner, the period of time between the first fuel entering the combustion chamber and the de-energizing of the quick-acting shut-off device if the flame monitor does not indicate a flame 3.28.3 main burner safety time: When there is an ignition safety time applicable to an igniter burner only the period of time between the first fuel of the main burner entering the combustion chamber and the de energizing of the quick acting shut-off device of the main burner if the flame monitor does not indicate a flame 3.28.4 extinction safety time: During operation of the burner the period of time between the extinction of the flame and the de-energizing of the quick-acting shut-off device 3.29 transfer station one or more lines each including a pressure control valve and a quick-acting shut-off device for the protection of the downstream supply lines and the connected appliances against overpressure The transfer station may comprise of heating and filtering equipment for the gas supply, measuring equipment for flow and calorific value and noise abatement devices Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) 4.1 Fuel supply General For multifuel firing systems using separate or combined burners these requirements shall apply to the oil and/or gas firing part involved Where several fuels are burnt simultaneously, improved safety measures can be necessary, especially in respect to limitation of heat input into the firing system and proper air supply to the individual fuels 4.2 Fuel transfer and preparation 4.2.1 The fuel supply line shall be equipped with a reliable quick-acting safety shut-off device (master fuel trip) which shall be positioned in a safe location It shall reliably cut off the fuel supply to the boiler room or the boiler area and shall be operable manually or by remote control or by an emergency switch (see 6.5) 4.2.2 Some liquid fuels, such as heavy fuel oil, require preheating to achieve the viscosity required for proper atomisation Where national oil quality standards are in existence, these shall be observed Any heat source other than open flames, that can be cut off immediately if required, and the rating of which can be automatically controlled, shall be used for oil preheating In the unpressurized condition the fuel oil temperature shall not attain the fuel oil flash point and in any case shall not exceed 90 C To attain the temperature for the required atomisation viscosity, pressure type preheaters shall be used The maximum temperature shall be at least C below the boiling temperature of water in the oil at the connected pressure Each fuel oil preheating system shall be automatically temperature controlled A temperature indicator shall be fitted downstream of the preheating system Oil temperatures below the temperature prescribed upstream of each burner or burner group shall shut off the burner or burner group Oil temperatures above the temperature prescribed upstream of the burners shall shut off the heat supply of the preheater or other suitable measures shall be taken For pressurized preheaters, the requirements for pressure vessels shall be applied Functioning of the necessary overpressure protection shall be ensured by suitable temperature control Any escaping oil shall be safely discharged Where steam heating coils for oil preheating are installed and the condensate is returned to the boiler, the heating coils shall be safely dimensioned and tested to ensure that no oil can escape into the condensate A means of checking the condensate for oil content shall be provided When steam lines are connected to fuel oil lines for purging purposes or for steam assisted atomisation, the line shall be protected against back flow from the higher pressured fluid 4.2.3 For gaseous fuels, a pressure controller shall be provided in the supply line to each firing system unless this task is performed by the transfer station The reliability of the gas pressure controller and its related safety device shall be proved by component testing or an individual test within the system acceptance test 4.3 Fuel lines 4.3.1 Fuel lines, including gaskets and valves shall be designed and laid out to withstand the mechanical, chemical and thermal loads to which they are exposed in service Only fire resistant piping material shall be permitted 4.3.2 The fuel lines shall be tight and properly fixed In systems subjected to vibrations the resulting stresses shall be minimized to avoid leakage 10 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) 4.3.3 Connections shall preferably be welded or brazed Threaded joints or bolted flanges shall also be used Welded joints shall only be made by welders approved to the appropriate standards (see EN 287-1) Brazed joints shall be permitted in oil lines for pipe diameters < DN 25 and/or operating pressure < 10 bar provided the brazers shall be approved and the filler materials have been certified, e.g by a certificate of a specialized manufacturer (see EN ISO 3677 and EN 1044) They shall also be permitted in gas lines for pipe diameter < DN 80 and/or operating pressure < bar For threaded joints the requirements of ISO 7-1 and ISO 228-1 shall apply Thread joints shall be used up to DN 50 and shall be sealed by metal to metal contact, or sealed by non-hardening sealing materials Hemp shall only be used as a sealant support The use of PTFE sealing materials shall be restricted as indicated in EN 751 Compression-type fittings in accordance with appropriate standards may be used up to DN 25, provided they shall be not to be dismantled for maintenance purposes Flanged connections on apparatus, equipment and valves shall be permitted for all diameters Material shall be in accordance with EN 13480-2 4.3.4 Flexible lines shall be used for connecting the burner to the fixed piping For fuel oil in the preheated state only jacketed metallic hoses shall be permitted Furthermore, flexible lines may be used instead of expansion joints at protected locations For oil, these lines should be jacketed metallic hoses, otherwise they shall be provided with a protective device consisting of e.g a double line with an oil monitor which switches off the oil supply pump in case of an oil leakage For gas, these lines shall be corrugated steel pipes All flexible lines shall be as short as possible, be readily visible, and shall be installed with adequate bending radii The flexible lines and the connections shall carry the manufacturer's symbols and indication of the nominal pressure The design pressure shall be at least 1,5 times the maximum allowable pressure The lines shall be protected against unacceptable external heating 4.3.5 To protect fuel lines against unacceptable high pressure, automatic control and safety devices shall be provided For oil lines, pressure relief valves shall be installed Protection of oil pumps and the effect of pressure rise in lines between closed shut-off devices due to heating shall also be taken into consideration For gas lines the necessary protection against overpressure shall be performed by a safety shut-off valve plus a pressure relief valve 4.3.6 On completion of installation, all fuel piping including valves and other equipment within the fuel lines up to the burner nozzles shall be cleaned to remove any weld spatter, corrosion products and foreign matter The type and performance of the cleaning process shall also be recorded In addition leakage testing and strength testing in accordance with a good engineering practice shall be performed For oil and gas, each safety shut-off device shall be subject to internal leakage testing, to confirm that fuels does not leak through the device After any welding work or replacement of components on fuel lines, the aforementioned tests shall be repeated The performance of the tests shall be authenticated by certificates recording the test procedure, the medium used, the test pressure and the test results obtained The certificates shall be issued by the person responsible for the testing 4.3.7 Gas escape lines for intermediate venting and for purging or charging shall be arranged such, that the escaping gas is either reliably ignited and burnt off with a flame trap installed in the pipe where the gases are transferred to the burning device or is safely discharged to the atmosphere if unburnt The joining together of these lines shall only permitted if no dangerous operating conditions are expected When necessary, gas escape lines shall be equipped with the necessary draining facilities Connections for test devices shall be provided so that the adequacy of venting can be checked For oil, intermediate drains shall be provided to ensure the safe discharge of escaping oil 11 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) Safety shut-off devices (Safety trip valves) 4.4 4.4.1 The fuel supply line shall be equipped with two safety shut-off devices arranged in series immediately upstream of each burner, or burner group One of these safety shut-off devices shall be of quick-acting design, and correspond with group A of EN 161 The second safety shut-off device may also be used as a fuel mass flow actuator for the control of the firing rate of the burner, but its closing time shall not exceed s For gas, these devices shall also correspond with group A of EN 161 The fuel supply lines shall be provided with devices for removing those impurities from the fuel which may impair the functioning of the safety shut-off devices The safety shut-off devices shall automatically and reliably cut off the fuel supply to the burner An adequate auxiliary power source, e.g a spring, shall be permanently available to assure this occurs The reliability of the automatic shut-off devices shall be proved This proof shall be performed by component testing as specified in EN 264 for liquid fuels or in EN 161 for gaseous fuels Leakage testing of each of the safety shut-off devices shall be possible in its installed condition at regular time intervals For gas, the connection line between these two safety shut-off devices shall be equipped with an intermediate venting or a leakage detection device Oil burners of special design such as return-flow atomizers, burners with a tip shut-off device etc., using return-flow lines shall be provided with additional double shut-off valves in these lines For gaseous fuels with low calorific value and with very low supply pressure, e.g below 200 mbar, the duty of the aforementioned safety shut-off devices may be performed by equivalent devices, e.g rotary slide valves with sealing water, or double-seat valves with an intermediate venting 4.4.2 The fuel supply shall not be released during the start-up operation until a) the ignition device is ready for ignition (see 6.1.5); b) purging is completed (see 6.5.2 and 6.5.3) or there is fire in the combustion chamber; c) the minimum preheating temperature required for the oil has been reached; d) the safety shut-off devices proved to be closed or the leakage test proved to be successful; e) the fuel control valve(s) and the air damper(s) are in the start position; f) functional control of the flame monitor proves no defect to be present, and in the case of individual flame monitoring detects there is no flame present prior to ignition 4.4.3 The automatic safety shut-off devices shall be operated such that they not release the fuel supply to the burners during the start-up operation, and cut it off during operation whenever 1) the control power for the safety devices fails; 2) the flue gas damper is not fully open or the induced draught fan fails, or the combustion chamber pressure is to high; 3) the combustion air fails to be supplied (see 5.1.1); 4) the combustion air flow is insufficient (see 5.2); 5) the pressure is: 12 a) the pressure of the atomising medium is less than that required (for steam and pressure-air atomizers), b) the fuel pressure is less than the minimum pressure (for gas burners, and oil burners with pressure atomizers), Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) c) the maximum fuel return flow pressure is exceeded (for oil burners with return-flow atomizers), 6) the speed of rotation of the atomising cup is insufficient (for oil burners with rotary atomizers) Where the atomising cup is on the same shaft as the fan, it will suffice to monitor the fan air pressure 7) there is an unacceptably high fuel flow rate in the burners; if necessary cut-off may be effected with a delay in time; 8) the ratio of flue gas recirculation flow/burner firing rate is unacceptable (see 6.2); 9) the flue gas recirculation fan, if fitted, fails and the ratio of flue gas recirculation flow/burner firing rate is unacceptable (see 6.2); 10) cut off switches are actuated; 11) the emergency switch is actuated (see 6.4.3); 12) any of the limiters responds (e.g for water level, temperature); 13) burners (also burner guns) which can be swung out or retracted without the aid of tools are swung out or retracted; 14) the flame monitor responds due to the absence or extinction of the flame 4.4.4 As soon as the causes for conditions a) to f) of 4.4.2 and 1) to 9) of 4.4.3 have been removed, the burners may automatically restart by following the regular start-up programme if this shall be permitted for the plant Where the conditions 10) to 14) of 4.4.3 apply, lock out shall always occur Restarting shall only be possible by manual intervention Where plants have multiple burners, if the conditions mentioned in 1), 3), 4), 5), 7), 8), 9), 10) and 14) of 4.4.3 occur only on one burner or one burner group, it shall suffice if the fuel supply to the respective burner or burner group is not released during start-up and is interrupted during operation This shall also apply to 12) of 4.4.3 if a hazardous escape of flames and flue gases is prevented 4.4.5 One manually operated emergency shut-off device shall be arranged immediately upstream of the burner, or each burner group A manually operated emergency shut-off device is for example: a stop cock; a stop valve provided the open cross-section can be completely closed by a maximum of two hand-wheel rotations; or an automatic safety shut-off device according to 4.4.1 if it can be additionally operated by hand at the location of operation 4.4.6 All safety related valves shall be durably marked with regard to their intended use Equipment for air supply and flue gas discharge 5.1 Air supply 5.1.1 The combustion air fan shall be monitored by the air flow and one of the following criteria: a) speed of the forced draught fan; b) pressure downstream of the forced draught fan; c) differential pressure at the forced draught fan; 13 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) d) power input of the forced draught fan motor 5.1.2 Where there are several burners with a common fan each shall be equipped with a pressure gauge or flowmeter in the air supply line This does not apply to burners with a common wind box 5.1.3 In the case of firing systems with several burners to which combustion air is supplied by a common control device, each burner shall be equipped with a shut-off device (e.g damper) in the air duct except when all burners fire in unison Shut-off devices in the air line to the burner shall be protected against unintentional mal-adjustment The positions during normal operation and ignition shall be checked In the case of interruption of fuel supply to the burner, this shut-off device shall also cut off the air supply automatically (if necessary, only to provide a minimum opening) This shall ensure sufficient air supply for the burners still in operation in the case of failure and shutdown of a burner or burner group The position of the shutoff device shall be identifiable In the case of interruption of fuel supply to all burners, it can be necessary to avoid the risk of implosion in the combustion chamber 5.2 Air/fuel ratio The air/fuel ratio shall be controlled within admissible limits The predetermined values of the air/fuel ratio and the admissible limits shall be stated in the operating manual The air/fuel ratio shall be monitored so, that in the case of unacceptable deviations from the ratio determined by the manufacturer of the firing system and defined within the operational instructions, the fuel supply is cut off The air/fuel ratio monitoring circuit shall be independent of the control circuit Monitoring shall not be required if the air/fuel ratio is controlled by mechanical means, and this ratio cannot be changed to exceed the admissible limits as a result of upset or operating conditions 5.3 Flue gas discharge 5.3.1 Flue gas discharge shall be monitored to ensure it is not unnecessarily restricted This shall be performed by the following measures: a) checking the position of the damper(s) during start-up; b) monitoring of the induced draught fan operation and combustion chamber pressure If the relevant combustion chamber pressure is exceeded the firing shall be cut-off and locked-out 5.3.2 The induced draught fan shall be monitored in accordance with 5.3.1 b) and one of the following criteria: a) speed of the induced draught fan; b) pressure upstream of the induced draught fan; c) differential pressure at the induced draught fan; d) power input to the induced draught fan motor; e) power circuit breaker of the induced draught fan motor 14 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) Firing system 6.1 Burners 6.1.1 The firing system shall be suitable for the respective boiler and may consist of a single burner or a multiple burner arrangement The task of the burners and the mode of operation of the burners are defined in 3.2 The requirements specified in clauses and shall be fulfilled by each individual burner Burners shall be individually tested (but see 6.1.3), at the latest during commissioning, or following any safety relevant modification to the firing system, and shall include: 1) verification of completeness of equipment according to the requirements of this standard; 2) functional testing of all safety-related equipment; 3) testing of burner management system in accordance with 6.4; 4) verification of maximum and minimum burner firing rate, including injection of additives, if used; 5) verification of flame stability during burner start-up, at the conditions given in 4) above, with the flue gas recirculation if any, and in the case of changes in firing rate, taking coincident combustion chamber pressures into consideration In all these cases, the flame shall be stable without significant pulsations; 6) evidence that the requirements for purging of flue gas passes and the safety times have been met; 7) proof that the required characteristic values relevant to combustion, such as CO2- or O2- if any, CO-content by volume, are obtained at the conditions given in 4) and at intermediate firing rates, if applicable In addition for oil burners unburnt particles (smoke) shall be checked 6.1.2 The burner individual test and the testing of the burner management system may be simplified by application of type tested equipment according to appropriate standards, e.g EN 225, EN 230, EN 267, EN 298, EN 676, if they fulfil the requirements described in 6.1.1 6.1.3 For multi-burner arrangements, the tests in accordance with 6.1.1 shall be performed collectively 6.1.4 Burners and their guns which operationally or without the aid of tools can be replaced, retracted or swung out, shall be provided with a locking device to cut out the supply of fuel and atomising medium (see 4.4.3, 12)) 6.1.5 Each burner shall be equipped with an igniter Admissible igniters are: 1) gas-electric igniters; 2) oil-electric igniters; 3) electric igniters The igniter shall provide a sufficient ignition source to light-up the main burner within the safety time It shall be ensured that the safety time of the main burner is not extended by influences of the ignition device 6.2 Flue gas recirculation 6.2.1 Flue gas recirculation shall not influence flame stability adversely Sufficient flame stability with maximum allowable flue gas recirculation flow shall be proven during burner test in accordance with 6.1.1 6.2.2 Where the flue gas recirculation flow is controlled as a function of the firing rate, the ratio of flue gas recirculation flow to burner firing rate shall be so monitored that the fuel supply is cut off if unacceptable deviations from this ratio, specified by the manufacturer of the firing system, arise The monitoring of the ratio of the flue gas recirculation flow to burner firing rate shall be independent of the control circuit Monitoring shall not be required if 15 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) the ratio of the flue gas recirculation flow to burner firing rate is controlled by mechanical means, and if this ratio cannot be changed to exceed the admissible limits as a result of upset operating conditions Acceptable deviations from the value predetermined for the ratio of the flue gas recirculation flow to burner firing rate shall be stated in the operating manuals The requirements given in 5.4 for the air flow shall be considered for the flue gas recirculation flow During start-up of a burner, particularly with a cold combustion chamber, flue gas recirculation shall not be initiated until flame stability and total combustion has been achieved e.g by a given minimum flue gas temperature or a minimum combustion air temperature 6.2.3 The requirements of 6.2.2 shall not apply to uncontrolled flue gas recirculation, if flame stability is proven at any firing rate and during start-up, see 6.1.1, 5) 6.2.4 6.3 If the flue gas recirculation fan fails, no reverse flow shall occur Control and monitoring 6.3.1 The firing system heat input shall be controlled automatically in relation to the heat demand To permit visual observation of igniter and main burner flames, inspection openings shall be provided at suitable locations at the combustion chamber or the burner(s) If escape of hot gases is possible, protection for personnel shall be provided 6.3.2 The suitability of control and monitoring devices relevant to safety which are specified in 4.4.3 shall be proved This may be done by individual testing or by the application of type tested equipment in accordance with appropriate standards, e.g EN 267, EN 298, IEC 60730-2-5 Individual components of control devices having safety functions shall meet the requirements of 6.3 6.3.3 Flame monitors shall be self-checking during operation 6.3.4 Flame monitors shall be designed and installed such, that checking by operating personnel can be performed at any time Functional testing shall be practicable without interfering with the electrical control system 6.3.5 In firing systems with multiple burner arrangements, the single-burner flame monitoring shall be replaced by a burner group or an overall combustion chamber flame monitoring system This may be achieved by providing master burners If flame failure is detected, all burners forming a group with a master burner, or the total of all burners in the combustion chamber shall be cut off by common safety shut-off devices, or their individual safety shut-off devices shall act jointly 6.3.6 The safety devices shall observe the safety times laid down in Table 6.3-1 for all types of burners when starting-up the burner, or when the flame extinguishes during operation Table 6.3-1 — Allowable safety times Type of burner Main burner Igniter burner Ignition safety time Extinction safety time s s 10 6.3.7 For large firing systems consisting of multiple burners with a firing rate of more than MW each in a common combustion chamber, the extinction safety time may be increased to a maximum of s for individual burners The ignition safety time shall in no case exceed the figures given in Table 6.3-1 for any firing system 16 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) 6.3.8 Gas-electric or oil-electric igniters shall be monitored independently of the main flame This can be accomplished by the main flame monitoring device provided the fuel supplies to both igniter and main burner shall be cut off when the main burner is not ignited within the safety time period 6.4 Electrical equipment 6.4.1 The electrical equipment of the firing system shall be provided in accordance with prEN 50156-1 6.4.2 To initiate a master fuel trip independently of the automatic control, at least one emergency switch shall be installed at a readily accessible and safe location, visible and durable marked 6.5 Safety precautions 6.5.1 The following safety functions shall be described in detail in the operating instructions in accordance with clause Prior to any firing system start-up, the flue gas passes shall be effectively purged The combustion cham6.5.2 ber and the flue gas passes shall be of such a design as to ensure effective purging To avoid ignition sources in an electrostatic precipitator, the precipitator voltage shall be brought down to half of the normal value during purging 6.5.3 For firing systems equipped with flue gas recirculation, the flue gas recirculation duct shall be included in the purging program of the combustion chamber and the flue gas passes for each start-up Generally, purging shall be performed as follows: the purging of the combustion chamber and the flue gas passes with the flue gas recirculation duct closed; the purging of the flue gas recirculation ducts may be commenced as soon as one part of the purging program for combustion chamber and flue gas passes has been performed, so that both purging operations can finish at the same time The purging of the flue gas recirculation ducts shall be performed with the flue gas recirculation damper at least 50 % open and with the flue gas recirculation fan running Three air changes of the volume concerned shall be considered sufficient 6.5.4 After every safety shut-off, purging shall be necessary prior to any restart NOTE Purging in accordance with 6.5.2 and 6.5.3 may be waived if special measures are taken to ensure that after cut out of the firing system no fuel is present in the combustion chamber and the flue gas passes, and it is also ensured that no fuel enters the combustion chamber during the outage 6.5.5 For burners requiring to be purged after shutdown, it shall be ensured that purged residual fuel will be safely ignited Safe ignition shall be, for instance, ensured if the required number of monitored master burners are in operation (see 6.3.5) NOTE After purging of the flue gas passes, the oil guns may be purged one after the other with the assistance of the ignition device in order to burn off the residual fuel A minimum air flow may maintained during purging of the oil guns 6.5.6 Upon completion of purging, the ignition process of the first burner shall be initiated within a period of 10 This period may be extended to 30 if, on completion of purging, an air flow of at least 20 % of the total combustion air flow shall be maintained 6.5.7 A second ignition of an oil burner or an attempt to ignite one other oil burner may be effected without intermediate purging within the times given in 6.5.6 A third ignition of the first oil burner shall be permitted for a furnace with three or more burners Re-ignition of gas burners shall not be permitted 6.5.8 When igniting a main burner the burner firing rate shall be limited so that the pressure shall not exceed the design value for the combustion chamber during the start-up operation 17 Licensed Copy: Institute Of Technology Tallaght, Institute of Technology, Thu Aug 23 10:11:54 GMT+00:00 2007, Uncontrolled Copy, (c) BSI EN 12952-8:2002 (E) 6.6 Common stack for several firing systems Flue gas flows from several firing systems shall only be joined in common ducts or stacks if an inadmissible pressure excursion resulting from the ignition of an explosive mixture is prevented This requirement will be met if the temperature of the flue gas is low enough to avoid selfignition, and if the influence of external ignition sources shall be prevented Unacceptable backpressure to the combustion chamber of the connected systems shall be prevented Operating manual An operating manual shall be provided with the boiler which indicates the schematic arrangement of fuel lines and valves, the test instructions for the flame monitors, the type of fuels to be used, the system maintenance requirements, the start-up and shutdown procedures for the burners as well as the measures to be taken when problems or dangerous condition arise Operational requirements are given in Annex B Particular requirements for firing systems burning gaseous fuels with high relative density 8.1 8.1.1 Main firing systems Supply of gases Gases in their liquid state shall only be supplied to the boiler room or boiler area if they are supplied to and burned in the burner in their liquid state Supply lines for gas in its liquid state shall be welded at the points of connection The piping and gun system downstream of the safety shut-off device shall be as short as possible If gases are supplied in their gasified state, a safety device shall be provided to ensure that no gas in its liquid state can enter the burner Only certified material shall be used for valves and gaskets 8.1.2 Safety shut-off device The components of the safety shut-off devices for heavy gas in its liquid state shall be tested in accordance with EN 264 8.1.3 Shutdown of burners for heavy gas in its liquid state After shutdown of the burner, the fuel supply line shall be purged from the safety shut-off device to the burner inlet A fixed connection for the purging medium shall be provided as close as possible to and downstream of the burner side safety shut-off device Failure of the purging medium supply during operation shall be indicated to the supervising personnel It shall be ensured that no gas can enter the lines carrying the purging medium For burners which are purged after shutdown, safe ignition of the purged liquid gas shall be ensured Safe ignition, is ensured if the required number of monitored burners is operating After simultaneous shutdown of all burners, the entire flue gas passes shall be adequately vented before purging the liquid gas line Pipes and burner guns shall only be purged if the ignition device is operating and sufficient air is available In the case of firing systems with several main burners, the individual pipes and burner guns shall be purged one after the other Gases may also be drained into the storage tank if the burner is equipped for this use In case proper shutdown is not performed automatically, a permanent instruction plate shall be provided at a readily visible location to indicate the sequence for start-up and shutdown of the firing system 18